User Commands                                         SLOW_PID(1)



NNNNAAAAMMMMEEEE
     slow_pid - the SLOW actuator PID loop

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     sssslllloooowwww____ppppiiiidddd,,,, [ifo=[IFO]]

MMMMAAAACCCCRRRROOOO OOOOPPPPTTTTIIIIOOOONNNNSSSS
     ifo=IIIIFFFFOOOO
          Replace IFO with the usual site name substitutions.  H2
          for  LHO2k,  H1 for LHO4k, L1 for LLO4k, C for Caltech,
          C1 for the 40m Lab and M1 for LASTI.


DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     _s_l_o_w__p_i_d is the SLOW actuator sequencer  that  implements  a
     software  proportional-integral-derivative  (PID) routine to
     keep the FAST actuator voltage to a small value.

     This  state  code  requires  the  EPICS   records   database
     _s_l_o_w_p_i_d._d_b to be loaded.  The MEDM screen is _s_l_o_w._a_d_l.

     The source state code is named "slpid.st" and compiles to an
     "slpid.o"  object  file.   The  program  name,  however,  is
     slow_pid.  Loading and execution of the state code  is  done
     thus:
                  ld < slpid.o
                  seq &slow_pid, "ifo=IFO"

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     Firstly  the  software  routine  is  only  active   if   the
     disable/enable  button  is set to "enable".  When activated,
     the loop will only make corrections if the reference  cavity
     transmission  is  higher  than  the  level set by the locked
     threshold slider on the MEDM screen.

     In the event that the laser drops  out  of  lock,  the  loop
     halts  and re-initializes all of its calculations.  In addi-
     tion, if for some reason the loop oscillates so  that  there
     is  a  drop  in  the reference cavity transmission, the loop
     also suspends.

     In case of network problems  and  the  number  of  connected
     EPICS  channels  is  less than the number of requested EPICS
     all calculations are re-initialized  and  the  sequencer  is
     suspended.

SSSSEEEETTTTTTTTIIIINNNNGGGGSSSS
     The locked threshold slider should not be set at the  actual
     level  of  the  reference cavity transmission, otherwise the
     software loop will not do anything.  The best setting  is  a
     value  above the reference cavity transmission when the loop
     is oscillating.



SunOS 5.9              Last change: LOCAL                       1






User Commands                                         SLOW_PID(1)



     The gain settings are best  done  experimentally.   Bear  in
     mind  that  the typical SLOW actuator coefficient is 4 GHz/V
     and the typical FAST actuator coefficient is 4  MHz.   There
     is  also  a factor of 499/2k in going from the EPICS control
     voltage to the SLOW actuator.  Note that the loop does noth-
     ing  if  the  various  gains are set to zero.  The loop time
     interval should be set to a value other than zero  in  order
     to avoid a "divide by zero" error.

     The reference cavity transmission EPICS channel should  have
     its  event  monitoring  field,  MDEL, set to be 0.010.  This
     means that the reference cavity transmission  should  change
     by  at least 10 mV before it generates an event.  Failure to
     do this will result in the event handler having  to  process
     too  many  events  and  after a short period of time the IOC
     will drop its network connections.   Any  smoothing  of  the
     reference  cavity transmission should also be avoided.  That
     is the SMOO field should be set to zero.


SSSSOOOOFFFFTTTTWWWWAAAARRRREEEE VVVVEEEERRRRSSSSIIIIOOOONNNN
     The version of the code is displayed  on  the  MEDM  screen.
     This  is  hard-coded in the state code and is assigned to an
     EPICS channel, PSL-FSS_SLOWVERSION.  Ideally this should not
     be changed via accessing the EPICS records database.


OOOOPPPPEEEERRRRAAAATTTTOOOORRRR SSSSCCCCRRRREEEEEEEENNNN
     Displayed on the MEDM screen are six sliders, one  each  for
     the  proportional  gain, integral gain, the locked reference
     cavity transmission threshold, the SLOW actuator adjust  and
     the loop time interval.  The monitoring points displayed are
     the reference cavity transmission and the FAST actuator vol-
     tage.


AAAAUUUUTTTTHHHHOOOORRRR
     Peter King

















SunOS 5.9              Last change: LOCAL                       2